The present invention relates generally to internal combustion engines, and more particularly to a cylinder head design, and specifically to a diesel locomotive engine built in consideration of the United States Environmental Protection Agency Tier-2 Emissions Standards.
It is well known to use a fuel injected diesel internal combustion engine as a power source for a locomotive. As a piston moves upward within a cylinder of a diesel engine, the air within the cylinder is compressed and heated. Fuel is injected into the combustion chamber as the piston nears its top dead center position. The fuel combusts with the compressed air, thereby providing energy for driving the engine and locomotive. There are many variables affecting the performance of a diesel engine, including the compression ratio, size of intake and exhaust valve openings, timing and duration of fuel injection, geometry of the combustion chamber, and peak temperature of the combustion gasses. In order to promote efficient operation of a diesel engine, it is known to optimize the size of both the intake and exhaust valve openings in order to reduce the pumping loop losses associated with the movement of the combustion and exhaust air. Because the cylinder wall is typically at a lower temperature than the piston top surface, it is also known to avoid the direct impingement of the injected fuel onto the cylinder wall because such fuel will not be completely oxidized during the combustion process. In order the minimize the loss of combustion heat through the cylinder wall and to minimize the amount of fuel that is impinged directly onto the cylinder wall, it is known to form a combustion chamber depression in the top surface of the piston in an area removed from the edges of the piston. One such design is illustrated in U.S. Reissue Pat. No. Re. 34,139 dated Dec. 8, 1992. An alternative design for maintaining the combustion gasses proximate the center of the piston is illustrated in U.S. Pat. No. 5,878,712 issued on Mar. 9, 1999. In this design a domed piston is provided with a dished depression which directs the combustion gasses away from the cylinder walls.
It is also known to utilize an anti-polishing ring in a diesel engine to prevent the formation of deposits such as soot and carbon around the top of the piston during operation of the engine. A small gap exists between the inside diameter of a cylinder and the outside diameter of the top of a piston. This gap defines a volume of relatively stagnant flow extending downward along the circumference of the piston to the level of the first piston ring. Deposits accumulating on the piston surfaces in this gap will reciprocate with the piston, thereby potentially causing wear in the cylinder/liner wall. U.S. Pat. No. 5,553,585 issued on Sep. 10, 1996, teaches an anti-polishing ring attached to the cylinder liner and having a diameter smaller than the remainder of the cylinder bore. The anti-polishing ring serves to remove deposits from the piston and to limit such deposits to a diameter smaller than that of the cylinder liner, thereby eliminating the potential for wear resulting from such deposits. However, the presence of an anti-polishing ring creates locations of increased stress, due to the presence of physical discontinuities and due to the variations in the relative heat transfer rates of the ring and the surrounding structures.
The United States Environmental Protection Agency has issued regulations directed to reducing the emissions from diesel locomotive engines. The Tier-2 Emissions Standards become effective on Jan. 1, 2005, and will require a significant reduction in the production of unburned hydro-carbons by diesel locomotive engines. To minimize the hide-out of unused air in the relatively stagnant volume around the top of the piston, it is desirable to reduce the size of the gap between the piston and the cylinder. However, the smaller the size of this gap, the greater the concern for wear of the cylinder caused by deposits in this area.